Dineutus, MACLEAY, 1825

Gustafson, Grey T & Miller, Kelly B, 2017, Systematics and evolution of the whirligig beetle tribe Dineutini (Coleoptera: Gyrinidae: Gyrininae), Zoological Journal of the Linnean Society 181 (1), pp. 118-150 : 129-131

GENUS DINEUTUS MACLEAY, 1825

( FIGS 1 , 4C , 5E , 6D , 7A–D , 8C , 9E, 9G , 11B–D , 13D )

Dineutus Macleay, 1825: 30 , type species Dineutus politus Macleay, 1825 .

S y n o n y m s: N e c t i c u s L a p o r t e, 1 8 3 5, D i n e u t e s Régimbart, 1882a.

Diagnosis: The genus Dineutus can be diagnosed within the Dineutini by the following combination of characters: (1) Gular suture complete, (2) frons without lateral bead ( Fig. 4C ), (3) antennal flagellum with 6–7 flagellomeres ( Fig. 5E ), (4) pronotal transverse impressed line present, (5) scutellar shield invisible with elytra closed, (6) protibia and male protarsi narrow ( Fig. 9E ), (7) mesotarsal claws sexually dimorphic, (8) metaventrite medially triangular in shape ( Fig. 6D ) and narrow and (9) female RT with vaginal shield ( Fig. 11B–D ) ( Brinck, 1980, 1983, 1984). The genus Dineutus lacks a single distinct autapomorphy among gyrinid genera. A character that comes close is sexually dimorphic mesotarsal claws, but this character is a synapomorphy shared with Porrorhynchus (and potentially Mesodineutes Fig. S9 ); however, the sexual dimorphism is most pronounced among species of Dineutus . The other synapomorphies with Porrorhynchus include the invisible scutellar shield and most noticeably the female RT possessing a vaginal shield. Dineutus can be readily distinguished from all other dineutine genera by the narrowed protibia, which is likely the sole apomorphy separating this genus from Porrorhynchus . Dineutus can be furthered distinguished from Porrorhynchus in having a complete gular suture and the pronotal transverse impressed line present.

Taxonomy: The genus was monotypic when originally erected by Macleay (1825). Régimbart subsequently treated the genus several times, revising it and adding many species ( Régimbart, 1882a, 1886, 1892, 1907). Hatch (1926) was the first author to divide the genus into subgenera, based primarily on overall body shape. Georg Ochs (1926, 1955) subsequently erected numerous subgenera, including subsuming Porrorhynchus as one of the subgenera. Since Ochs’ work, no new subgenera have been proposed, but the composition of the subgenera has been re-arranged by Guignot (1950), and most recently by Brinck (1955b), who attempted to provide distinct morphological traits identifying each subgenus, unsuccessfully.

There are currently 92 species within the genus Dineutus , making it easily the largest genus within the Dineutini .

Distribution: Dineutus has a near global distribution, missing from Europe, and most notably from South America ( Fig. 14D ) ( Mouchamps, 1949b; Brinck, 1955b, 1976; Satô, 1962; Mazzoldi, 1995; Watts & Hamon, 2010; Hájek & Reiter, 2014; Gustafson & Miller, 2015; Lee & Ahn, 2015). Currently, the highest diversity is in the Austral region, primarily in New Guinea, but this likely reflects bias due to recent taxonomic work on species in this region (i.e. Brinck, 1976, 1981, 1983, 1984). The second highest diversity is found in tropical Africa.

Discussion: This is the largest and most widely distributed genus within the Dineutini .

Figures

Figure 1. Phylogeny of the Dineutini based on Bayesian tip-dating analysis Part 1. Labels at node denote posterior probability, blue bars indicate 95% hpd for age. The blue clades indicate members of Dineutus, with lighter blue showing the subgenus Cyclous sensu nov. and the dark blue the Dineutus s.s. subgenus. Purple indicates the genus Porrorhynchus. Species are approximately to relative scale.

Figure 4. Head capsules of dineutine species, anterior view. Scale bars = 1 mm. Abbreviations: lbr, labrum: cly, clypeus: frb, frontolateral bead. (A) Enhydrus sulcatus; (B) Macrogyrus (Macrogyrus) australis; (C) Dineutus (Cyclous) australis; (D) M. (Andogyrus) seriatopunctatus; (E) Porrorhynchus landaisi; (F) M. (Cyclomimus) purpurascens.

Figure 5. Antennae of dineutine species: above, anterior view; below, posterior. Scale bar = 0.5 mm. (A) Macrogyrus (Macrogyrus) australis; (B) M. (Andogyrus) zimmermanni; (C) Porrorhynchus landaisi; (D) Enhydrus tibialis; (E) Dineutus (Cyclous) australis.

Figure 6. Meso- and meta-ventrites of dineutine species and a gyrinine species, ventral view, scale bars = 1 mm, except (F). (A) Enhydrus sulcatus; (B) Macrogyrus (Andogyrus) colombicus; (C) Porrorhynchus marginatus; (D) Dineutus (Cyclous) carolinus; (E) Mesodineutes amurensis†; (F) Gyrinus maculiventris, scale bar = 0.5 mm.

Figure 7. Protrochanters of male dineutine species, ventral view. Abbreviations: ts, protrochanteric setae; wx, waxy spot; pt, protrochanteric setose patch. (A) Dineutus (Cyclous) australis, scale bar = 200 µm. pb, protrochanteric brush; (B) Dineutus (Cyclous) proximus, scale bar = 500 µm; (C) D. (Dineutus) ‘n. sp.’ Scale bar = 300 µm; (D) D. (Cyclous) serrulatus analis, scale bar = 300 µm; (E) Porrorhynchus marginatus, scale bar = 400 µm; (F) Macrogyrus (Macrogyrus) albertisi, scale bar = 500 µm.

Figure 8. Prolegs of male dineutine species. Abbreviations: sb, setose brush; asr, anterior row of profemoral setae; psr, posterior row of profemoral setae; sp, setigerous puncture. (A) Macrogyrus (Andogyrus) zimmermanni protibial apex, posterior view, scale bar = 400 µm; (B) Porrorhynchus marginatus protibia, posterior view, scale bar = 500 µm; (C) Dineutus (Cyclous) australis protrochanter and profemur, ventral view, scale bar = 500 µm; (D) M. (A.) zimmermanni protrochanter and profemur, ventral view, scale bar = 1 mm.

Figure 9. Protarsus of male dineutine species. Abbreviations: di, protarsal discus; sb, setose brush. (A) Macrogyrus (Andogyrus) zimmermanni, scale bar = 500 µm; (B) M. (Macrogyrus) sp., scale bar = 500 µm; (C) M. (M.) albertisi, scale bar = 500 µm; (D) Porrorhynchus marginatus, scale bar = 1 mm; (E) Dineutus (Dineutus) ‘n. sp.’, scale bar = 1 mm; (F) Enhydrus atratus, scale bar = 2 mm; (G) D. (Cyclous) australis, scale bar = 500 µm.

Figure 11. Female reproductive tracts, ventral view. Abbreviations: sp, spermatheca; fd, fertilization duct; ov, common oviduct; bu, bursa; lt, laterotergite; vs, vaginal shield; mp, medial apodeme of gonocoxa; gc, gonocoxa; scale bars = 1 mm. (A) Porrorhynchus landaisi; (B) Dineutus (Dineutus) tetracanthus; (C) D. (Cyclous) discolor; (D) D. (Rhomborhynchus) depressus.

Figure 13. Sperm of dineutine species, exhibiting primary conjugation via spermatostyles. (A) Enhydrus atratus, scale bar = 300 µm; (B) the same, scale bar = 50 µm; (C) the same with single sperm, scale bar = 20 µm; (D) Dineutus emarginatus, scale bar = 50 µm; (E) Macrogyrus (Macrogyrus) rivularis, scale bar = 100 µm; (F) Porrorhynchus marginatus, scale bar = 100 µm.

Figure 14. General distribution maps of dineutine genera. (A) Dineutus; (B) Porrorhynchus); (C) Enhydrus; (D) Macrogyrus.